Proposal-based approaches One line of these approaches [1]}, [2]}, [3]} solve instance segmentation within a two-stage manner, by first propose regions of interests (RoIs) and then regress the semantic labels of pixels within them. The drawback of these approaches comes from the loss of objects by NMS due to large IoU. Instead, works like [4]} tackle the problem within a single-stage manner. For example, PolarMask [4]} models the contours based on the polar coordinate system and then obtain instance segmentation by center classification and dense distance regression. But the convex hull setting limits its accuracy.
